1. Field of the Invention
The invention relates generally to improving some radiation characteristics of horn antennas by loading the antennas with low-loss dielectrics. More specifically, the invention relates to horn antennas loaded in the transverse plane and in the longitudinal plane with low-loss dielectrics in order to improve beam sharpening, axial gain and other radiation characteristics. The invention also relates to a line-of-sight portable communication system employing the characteristics of dielectric-loaded horn antennas.
2. Description of Prior Art
Antennas are broadly grouped into two categories, wire or aperture antennas. Aperture antennas are those having a feed waveguide and an antenna characterized by the geometry of the aperture, such as parabolic, conical, horn, etc. The bulk of conventional aperture antenna design has concentrated on unloaded antennas, that is, where the aperture has no insert of any kind within the aperture. However, where the disadvantages of dielectric inserts, such as higher side lobe level or increased frequency sensitivity can be tolerated, dielectric loading can provide beam narrowing, lowered input voltage standing wave ratio (VSWR) and non-mechanical beam scanning. The critical parameters when designing dielectric loaded antennas are the dimensions, shape, volume, dielectric constant homogeneity, location and orientation of the insert(s) within the antenna of use. Although the foregoing is broadly applicable to all aperture antennas, the present invention is primarily concerned with improved designs of H-plane sectoral horn antennas loaded either with arrays of dielectric slabs in the transverse direction i.e., perpendicular to direction of electromagnetic propagation, or with dielectric wedges in the longitudinal direction. In each embodiment, addition of the dielectric attenuates radiation power but serves to increase efficiency of the attenuated radiation power.